The traditional poppet valves fitted to the ports of an internal combustion engine are reliable and durable, and capable of withstanding the pressurized compression of the chamber and the subsequent explosion of the air fuel mixture. However, such valves are not amenable to adjusting or metering the flow of the air fuel mixture with the reciprocating motion that is produced by a fixed cam or pushrod profile. Whereas an iris shutter can be amenable to adjusting or metering the flow, it does not withstand the explosion of the combustion chamber. Thus by combining these two, the best feature of each can be used to produce the ideal intake and exhaust valve design.
Reference can be made to U.S. Pat. No. 4,094,492 issued Jun. 13, 1978 for an example of a variable orifice iris shutter system for controlling gas flow.